Significance. Many low vision patients have impaired central acuity but cannot successfully use telescopic spectacles despite the theoretical benefit from magnification. this may be because visual rehabilitation with telescopic spectacles is limited by instability of the magnified retinal image during involuntary head movements, and during coordinated eye-head movements necessitated by visual search. Retinal image stability is ordinarily provided by the visual-vestibulo-ocular reflex (VVOR), produced by interaction of the vestibulo-ocular reflex with visual and predictive mechanisms (visual-vestibular interaction, VVI). VVOR performance with telescopic spectacles must be quantitatively appropriate to magnification to avoid substantial impairment of dynamic visual acuity during head movements. Despite this importance, knowledge is lacking regarding the effects of aging and pathologic factors on human vertical VVI. Aims and Methods. The overall aim is to quantitatively evaluate mechanisms of VVI in the vertical plane, as determinants of useful vision with telescopic spectacles during physiologic head movements. Eye and head movements will be measured using magnetic search coils. The effect of telescopic spectacles on vertical VVOR will be quantitatively characterized in the physiologic range of active and passive head velocities and frequencies, in normally sighted and low vision adults. Findings will be correlated with separate measurements of visually guided tracking. The effects on VVI and tracking of unpredictable motion, reduced luminance and contrast, aging, pathologic nystagmus, and visual field defects will be studied. The relationship between instantaneous vertical retinal image slip velocity, and dynamic visual acuity, will be studied in relation to viewing strategies employed with telescopic spectacles. By studying horizontal and vertical eye and head movements during unrestrained visual search, experiments will identify characteristics of optimal visual search strategies with telescopic spectacles. Modification of search strategy to minimize retinal image instability and search time will also be evaluated. This data will enhance basic understanding of human vertical eye movements, and provide clinical insight into an important problem in clinical low vision.